ATYPICAL RESPONDERS LANDSCAPE REVIEW ∙ OCTOBER, 2017 14 context under investigation. Patients exhibiting an atypical response as per these three categories may have MBC or another life-limiting disease. Exceptional responses may be quantitative (i.e., tumor shrinkage, absence of new metastases) or related to duration of response. Mechanisms of rapid progression may include intrinsic or acquired resistance [11, 12]. Patients on conventional therapy as well as those in clinical trials should be included when studying atypical responses, because a community-based population will generally be more heterogeneous than a population enrolled in a trial. BENEFITS OF STUDYING ATYPICAL RESPONSES Clear categorization of subgroups of atypical responders is needed to allow prospective selection of patients for hypothesis testing and to allow comparison of results across studies. Once the response of the patients being studied is more clearly stated, researchers can then determine the underlying reasons as to why the response occurs. These categories will also improve the potential for data sharing and accelerating research. Studying patients exhibiting an atypical response may provide mechanistic insight, increase researchers’ understanding of tumor and other biomarkers, and lead to novel combinatorial therapeutic strategies [9, 13-15]. Such studies are expected to provide experts with improved information, which in turn will enhance the domain of personalized medicine that is already part of best practices for MBC and many other illnesses. Because a single given therapy may not benefit a largenumberofpatients,studyingpatientswhoexhibitanatypicalresponsewilllikelyprovideagreater understanding of the phenomenon, identify novel biomarkers that can be used to prospectively identify patients who will [11-14, 16-18] and will not [13] benefit from a particular therapy, and lead